A solution for an issue with dlopen

[Iximiel]

Hi all,

TL;DR: if you have a strange segfault on getenv calls, try to run plumed after export PLUMED_LOAD_DLCLOSE=no (thanks, @GiovanniBussi )

I was working on the interface to plumed for external codes and I found this curious behaviour:
When you check that plumed is available to use and plumed it is not found the next time you call getenv to look for a non-existent environment variable you get a segmentation fault 😨

Luckily this happens only with a determinate software configuration (this is fun) and can be solved by simply exporting export PLUMED_LOAD_DLCLOSE=no before running the plumed-patched program

The minimal code to reproduce the issue is this spoiler

#define __PLUMED_WRAPPER_FORTRAN 0
#define __PLUMED_WRAPPER_LINK_RUNTIME 1
#define __PLUMED_WRAPPER_EXTERN 0
#define __PLUMED_WRAPPER_CXX 1
#define __PLUMED_WRAPPER_LIBCXX11 1
#define __PLUMED_WRAPPER_LIBCXX17 1
#define __PLUMED_WRAPPER_IMPLEMENTATION 1
#define __PLUMED_HAS_DLOPEN

#include "Plumed.h"
#include <cstdlib>
#include <iostream>

void mygetenv(std::string var) {
    auto val = getenv(var.c_str());
    if (val)
       std::cout << var << ": "<< val << "\n";
    else
       std::cout << var << " not FOUND!!\n";
}

int main() {
    mygetenv("PLUMED_KERNEL");
    mygetenv("PLUMED_KERNEL_");
    std::cout << "Plumed is " << (PLMD::Plumed::installed()?"":"not ") << "installed\n";
    mygetenv("PLUMED_KERNEL");
    mygetenv("PLUMED_KERNEL_");
    return 0;
}

all: test

test: test.o
	g++ -o test test.o -ldl
test.o: test.cpp Plumed.h
	g++ -c test.cpp

Plumed.h:
	wget https://raw.githubusercontent.com/plumed/plumed2/refs/tags/v2.10b/src/wrapper/Plumed.h

clean:
	rm -fv *.o test